Re: [9front] srv(3) clone and srvid

[Jacob Moody <moody@mail.posixcafe.org>]

On 3/29/23 14:15, unobe@cpan.org wrote:
> Quoth ori@eigenstate.org:
>> Quoth Jacob Moody <moody@mail.posixcafe.org>:
>>> Yes, clone works like how it does in /net, the board is only open for as long
>>> as you have the fd open. So you cat'd it which opened it, read the new id, then closed
>>> it deallocating the child srv. You need to keep the fd open for the length of time you
>>> use the child srv, Or if you wish to 'pin' the child srv you can stash the clone fd itself
>>> as a file in the child srv. This will keep the child srv around until you remove the pinned
>>> clone fd.
> 
> Thank you Moody. I'm still misunderstanding something because I would have that:
> 	 bind -c '#s20' /srv
> when /srv/20 isn't available would have failed somehow, since the man page states:
>     As a convention, /lib/namespace
> 	accepts the path to the service directory from the environ-
> 	ment variable $srvspec, making it possible to start a new
> 	namespace using a specific service directory as a starting
> 	point.
> 
> But for comparison, this has no failure either:
> 	bind '#l20' /net
> so I still need to wrap my head around something.


#s20 and $s/20 are different things. The first is an attach argument,
the second is access the sub directory 20.

> 
>> for an example of how it's used on shithub:
>> 	
>> 	<[3]/srv/clone{
>> 		d=`{<[0=3]read}
>> 		bind /srv/$d /srv
>> 		# ugly, but we don't want to leak the clone fd into
>> 		# procs that may stick around, so write over fd3 again
>> 		<[3=0]{
>> 			rfork n
>> 			bind /usr/web /mnt/static
>> 			execfs -m /usr/web /sys/lib/tcp80/gitrules
>> 			bind /mnt/static /usr/web/static
>> 			rfork n
>> 			cd /
>> 			exec /bin/tcp80
>> 		}
>> 	}
>>
> 
> Thank you Ori, that was very helpful.  I was surprised to see that the
> file is left open when there's an rc error:
> 	cpu% lc /srv
> 	acme.glenn.3372	cons			hjfs.cmd		rio.glenn.504
> 	acme.glenn.908	cs				mntexport		rio.glenn.836
> 	boot			dns				pin-glenn		slashmnt
> 	clone			factotum		plumb.glenn.495	slashn
> 	cpu% </srv/clone { d=`{<f} }
> 	/fd/0:2: < can't open: f: 'f' not found
> 	cpu% lc /srv
> 	36/				cons			mntexport		slashmnt
> 	acme.glenn.3372	cs				pin-glenn		slashn
> 	acme.glenn.908	dns				plumb.glenn.495
> 	boot			factotum		rio.glenn.504
> 	clone			hjfs.cmd		rio.glenn.836
> 	cpu% bind -c '#s36' /srv
> 	cpu% lc /srv
> 	36/				cons			mntexport		slashmnt
> 	acme.glenn.3372	cs				pin-glenn		slashn
> 	acme.glenn.908	dns				plumb.glenn.495
> 	boot			factotum		rio.glenn.504
> 	clone			hjfs.cmd		rio.glenn.836
> 	cpu% bind -c '#s'/36 /srv
> 	cpu% lc /srv
> 	clone
> 
> When the window is closed, then 36/ finally is cleaned up.
> 
> 
This seems like an rc bug that is leaking the file descriptor.